I just started up my A4 after a minor rebuild. After running for about 20 seconds I noticed that the thermostat housing was leaking from around the gasket.

What would cause this???

A little background - I replaced all of the head studs except for 3 of them that wouldn't come out. One of those studs was for the therm housing. When I put the head back on, I didn't notice if that one particular stud was spinning when I tightened everything back up. Now, it does seem a bit taller than the others...but that could be my imagination.

My initial thoughts are that the stud was slowly pulling out when I tightened them up.

Did you remove the T-stat housing from the head?
You might just need a new gasket for the T-stat.
Moyer recommends only putting gasket sealer on 1 side of the T-stat gasket. This way it is removable without always replacing the gasket.
It could also be the stud you mentioned. Perhaps that needs some gasket material.
Good luck.

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It would be better to check the status of that stud. Moyer recommends putting the sealer on one side -- the housing side -- so that one can take the thermostat housing off the head without tearing the gasket. Having sealant on only one side of the gasket isn't going to cause a leak unless there's another issue.

Make sure to remove the old gasket as completely as possible before putting the new one on.
Afourians tend to be a bit anal about different kinds of gasket sealers. Permatex or pemetex seems to be a favorite that comes in a few different flavors. I have successfully used the generic black gasket paste you will find at any auto parts store.
Like SemiJim suggests, the gasket paste needs a short amount of time to set before you try using your new seal.
Check and seal the stud by all means but if water is leaking out from the T-stat housing and the head there is most likely something wrong with your gasket (like no gasket paste).
This stuff is used on airplanes and cars: http://www.permatex.com/products/aut..._Sealant_a.htm

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